Charlie and the Chocolate Factory Theatre Royal, Drury Lane Children’s authors and entertainers customarily assert that children are always their fiercest critics. My daughter, nearly six, loved the director Sam Mendes and writer David Greig’s Charlie and the Chocolate Factory. She loved it so much that she asked at the end – perhaps mistaking the theatre for a DVD – if she could see it all over again. With the best seats going for almost £70, that would always have been unlikely. Having sat through it with her, I fear the producers would have to pay me handsomely to make a return visit. This vastly disappointing, hugely expensive musical almost kills Roald Dahl’s dubious classic. Children (or perhaps just my one) lack critical facilities, I must conclude.

But they are right to like Dahl, because his work is funny, eccentric and vivid and never worries about what grown-ups will think of it. This gives this Charlie the same advantage enjoyed by the adaptation of Dahl’s Matilda. Nevertheless, its makers face huge problems given that Charlie, played remarkably well at my matinee by 12-year-old Jack Costello, is a dull goody-goody. The interest is in Willy Wonka, who owns the factory – and in the factory itself, a vast theme park that’s literally good enough to eat. Studio lots and CGI made this possible to realise on film, in 1971 and in 2005. But it was always going to be a challenge for a theatre, even for one as large as the Theatre Royal.

At first I felt in safe hands. Cut into the unraised curtain was a framed cocoa bean from which the fantasy would surely grow as certainly as Jack’s beanstalk. Next came an animated doodle explaining the chocolatemaking process. Then we opened on the Bucket family, who are not only poor, as they are in the book, but now live on a scrapheap, neatly ducking any housing-benefit questions and also suggesting the play’s ultimate theme that something can come out of little, given enough imagination. I liked one other subversive touch, the street-seller with her anti-confectionery message that chocolate “gives you the trots and lots of spots”.

From there, the production lost pace as weak dialogue from Charlie’s Grandpa Joe (Nigel Planer) and the other Very Old People failed to raise laugh after laugh. The remainder of the act was spent watching, on a giant mock TV, the four other child winners of the golden tickets to Wonka’s open day, singing of their sins (gluttony, TV addiction etc). The wait for Charlie to find his own ticket drags even in the book. Here, I prayed for Charlie to find the damn thing and set things going. When he finally did, the curtain fell.

The second half , which takes us inside the factory, had to be a series of greatest-ever transformation scenes. But the chocolate room was dim and aquatic, like a tourist shop snowscene. Its waterfall was static. The pipe up which Augustus Gloop was sucked was industrial iron, not glass.The inventing room looked like a branch of Yo! Sushi. And so on. It would be unreasonable to expect 100 squirrel nut-testers to attack Veruca Salt, but here a handful of blokes dressed in squirrel suits have a punch-up as if on Harry Hill’s TV Burp. As for the Oompa-Loompas, the union of dwarf actors should sue for loss of work.

The threadbare trickery would not have mattered had the personality of Wonka and the power of the music sufficiently stimulated our willing suspension of disbelief. But Douglas Hodge’s Wonka was only adequate, lacking either Gene Wilder’s distracted zaniness or Johnny Depp’s damaged mania. He sang “Pure Imagination” better than Wilder – just as well, as it was the best number in the production. A couple of Scott Wittman and Marc Shaiman’s original songs – “Strike That! Reverse It!” and “Simply Second Nature” – had lyrical potential but remained stubbornly unhummable.

Again and again, I wished Mendes and his team had spent more time in the Inventing Room. Or perhaps they spent months there and inspiration never struck. Willy Wonka, like God, supplies temptation to his children and punishes them if they fail to resist it. Mendes could not resist the lolly either and he too has been punished. His show all too plainly lacks the one thing that redeems Charlie: imagination.

The cast of Sam Mendes's Charlie and the Chocolate Factory. Photograph: Helen Maybanks.

Andrew Billen has worked as a celebrity interviewer for, successively, The Observer, the Evening Standard and, currently The Times. For his columns, he was awarded reviewer of the year in 2006 Press Gazette Magazine Awards.

Bertie Carvel's diary: What would the French think about infidelity to Doctor Foster?

According to the adage, the first thing an actor does when he gets a job is to go on holiday. And so, having finished our sold-out run of James Graham’s Ink at the Almeida and with the show (in which I play a young Rupert Murdoch) about to transfer into the West End, I’m packing my bags.

But before I can skip town, I’ve one more professional engagement: the press launch of series two of the BBC drama Doctor Foster, which we finished filming at Christmas. I’ve now seen the final cut of all five episodes, and I’m excited to share it with an audience. There’s no substitute for seeing other people’s reactions at first hand, especially with a show that got people talking so much first time around, and it’s electric to sit in a cinema full of expectant journalists and commentators and feel the room respond. Nothing beats this: to put so much into making a thing and then experience an audience’s unmediated, reflexive reaction. When it goes well, you feel that you’ve shared something, that you’ve all recognised something together about how things are. It’s a unifying feeling. A sort of bond.

Cheating spouses

Handling the interviews has been tricky, when there’s so little one can say without giving the plot away. (The first series began with Suranne Jones’s character Gemma, a GP, suspecting her husband Simon of having an affair.) What’s more, lots of the questions invite moral judgements that I’ve tried my best to avoid; I always think it’s really important not to judge the characters I play from outside, but simply to work out how they feel about themselves, to zero in on their point of view. There’s a sort of moral bloodlust around this show: it’s extraordinary. People seem to want to hear that I’ve been pilloried in the street, or expect me to put distance between myself and my character, to hang him out to dry as a pariah.

While I’m not in the business of defending Simon Foster any more than I’m in the business of attacking him, I am intrigued by this queer mixture of sensationalism and prurience that seems to surface again and again.

Shock horror

Oddly enough, it’s something that comes up in Ink: many people have been surprised to find that, in a story about the re-launch of the Sun newspaper in 1969 as a buccaneering tabloid, it’s the proprietor who considers dropping anchor when the spirit of free enterprise threatens to set his moral compass spinning.

I’ve never given it much thought before, but I suppose that sensationalism relies on a fairly rigid worldview for its oxygen – the SHOCKERS! that scream at us in tabloid headlines are deviations from a conventional idea of the norm. But what’s behind the appetite for this sort of story? Do we tell tales of transgression to reinforce our collective boundaries or to challenge them?

For me there’s a close kinship between good journalism and good drama. I’m reminded of the words of John Galsworthy, who wrote Strife, the play I directed last summer, and who felt that the writer should aim “to set before the public no cut-and-dried codes, but the phenomena of life and character, selected and combined, but not distorted, by the dramatist’s outlook, set down without fear, favour, or prejudice, leaving the public to draw such poor moral as nature may afford”.

So when it comes to promoting the thing we’ve made, I’m faced with a real conundrum: on the one hand I want it to reach a wide audience, and I’m flattered that there’s an appetite to hear about my contribution to the process of making it; but on the other hand I think the really interesting thing about the work is contained in the work itself. I’m always struck, in art galleries, by how much more time people spend reading the notes next to the paintings than looking at the paintings themselves. I’m sure that’s the wrong way around.

Insouciant remake

En route to the airport the next morning I read that Doctor Foster is to be adapted into a new French version. It’s a cliché verging on racism, but I can’t help wondering whether the French will have a different attitude to a story about marital infidelity, and whether the tone of the press coverage will differ. I wonder, too, whether, in the home of Roland Barthes, there is as much space given to artists to talk about what they’ve made – in his 1967 essay, “The Death of the Author”, Barthes wrote that “a text’s unity lies not in its origin but in its destination”.

No stone unturned

Touring the villages of Gigondas, Sablet and Séguret later that evening, I’m struck by the provision of espaces culturels in seemingly every commune, however small. The French certainly give space to the work itself. But I also notice a sign warning of a chat lunatique, so decide to beat a hasty retreat. Arriving at the house where I’m staying, I’ve been told that the key will be under a flowerpot. Lifting each tub in turn, and finally a large flat stone by the door, I find a small scorpion, but no key. I’m writing this at a table less than a yard away so let’s hope there won’t be a sting in this tale.

Ink opens at the Duke of York Theatre, London, on 9 September. More details: almeida.co.uk